Problem: Which of these numbers is composite? ${3,\ 23,\ 34,\ 43,\ 61}$
Solution: A composite number is a number that has more than two factors (including 1 and itself). 3, 23, 43, and 61 each have only two factors. The factors of 34 are 1, 2, 17, and 34. Thus, 34 is the composite number.